1. Field of the Invention
The present invention relates to a secondary battery having a hard case that is integrally formed resulting in a reduced number of parts and a simplified fabrication process.
2. Description of the Related Art
Unlike the primary battery that is not rechargeable, the secondary battery is rechargeable and dischargeable for dozens of times. Secondary batteries are widely used in portable electronic apparatuses, such as cellular phones, laptop computers, camcorders, and even hybrid vehicles.
The type of the secondary battery is determined based on materials used for the positive electrode plate and the negative electrode plate, the appearance of the battery, or its application. The shape of the secondary battery can be either cylinder type or square type. The square type secondary battery has an electrode assembly received within a flat can. The square type secondary battery is produced by attaching a circuit unit, a case, and a label on the outside of the bare cell, where the bare cell includes an electrode assembly and a cap assembly inside the can.
For a secondary battery, more than two kinds of materials are used in producing the case, thereby increasing the fabricating cost. Specifically, a hard case, which was manufactured in advance, protects a part of the can. A part of the hard case and a part of the can form a molding case by using hot molten resin. To achieve this, processes of manufacturing two hard cases, attaching a hard case to a can, and molding by the use of hot molten resin are needed. However, the bare cell often breaks during the molding process because the bare cell, which accommodates an electrode assembly, an electrolyte, and a cap assembly inside a can, is directly influenced by the molding process, thereby deteriorating the yield. For example, there are various reasons for breakage of the bare cell, such as breakage from inserting the bare cell into a mold to form a molding case, breakage by heat when applying a hot molten resin, and breakage by pressure of a mold, thereby deteriorating the yield and increasing the fabricating cost.
Furthermore, additional space for the bare cell is required when manufacturing a mold, thereby increasing costs for manufacturing a mold. It is also a problem that the molding process can only be performed after the bare cell has been attached to the hard case. As a result, it is not easy to remove the case after finishing the molding process when there is something wrong with the circuit module. Therefore, it is not feasible to recycle the bare cell, even if the bare cell has no defects.